This invention relates to compositions of matter classified as coatings, where thicknesses of said coatings are governed by the methods of application. More specifically this invention relates to coatings applied to metal surfaces, where both the coating and the metal possess functional groups that react with epoxide groups, and the method of application is by powder coating methods or melt processing methods or liquid methods. Still more specifically, this invention relates to amide containing resins applied by powder coating methods or melt processing methods, and fluoropolymer based resins applied by liquid methods.
This invention enables the strong attachment of coatings to substrates (this strong attachment is ordinarily embodied as good adhesion and good resistance to corrosion), while at the same time minimizing deleterious environmental effects from its use.
For a great many uses, in order to obtain strong attachment of coatings to the surfaces on which they are applied, particularly metal surfaces, a primer is used. This is especially true for resin systems comprising amide groups, in particular resin systems comprising substantially polyamide 11 or polyamide 12 applied by powder coating methods or melt processing methods. It is likewise especially true for resin systems comprising substantially poly(vinylidene fluoride) applied by liquid methods. If additional corrosion resistance is desired, a corrosion inhibitor such as a chromium compound, is placed in the primer. Since chromium compounds are considered as health risks, and their use is strictly legislated, elimination of their use is desirable.
To applicant""s knowledge, all such primers for resin systems comprising substantially polyamide 11 applied by powder coating methods are organic solvent based and contain epoxy compounds. Corrosion inhibitors used in such primers ordinarily contain chromium compounds. No art is known which suggests that an aqueous based epoxy compound containing primer composition can be substituted successfully for organic solvent based epoxy primers, much less that such substitution will allow elimination of the chromium containing anti-corrosion agents without sacrificing adhesion or corrosion resistance.
Such substitution is desirable because it enables reduction of the emission of volatile organic compounds (VOCs) inherent in the use of the present organic solvent based primers and the elimination of the presence of toxic chromium containing compounds.
The invention provides in a first process aspect, an improved process for priming a metal surface to improve the adhesion to said surface, and other properties, of resin coatings which possess functional groups that react with epoxide groups, wherein the improvement comprises applying an emulsion in water of a polyfunctional epoxide compound to said surface. Such resin coatings include, but are not necessarily limited to, amide containing resins applied by powder coating methods or melt processing methods, and fluoropolymer-containing resins applied by liquid methods.
The tangible embodiments produced by the first process aspect of the invention possess the inherent applied use characteristics of improving the wetting and adhesion of said coatings. In addition, the improvements are provided with emissions of VOCs, if any, in a range well below that required by present air quality regulations and well below that required by any such regulations presently foreseeable in the future. The tangible embodiments also provide for enabling improved corrosion resistance for the metal substrate to which the coating is adhered without the use of toxic chromium compounds.
Special mention is made of those aspects of the first process aspect of the invention wherein the polyfunctional epoxide compound is a substantially difunctional epoxide.
The invention provides in a first composition aspect, a metal object having on at least one surface a primer coating prepared by the first process aspect of the invention.
The invention provides in a second process aspect, a process for the application of an adherent coating based on amide containing resins applied by powder coating methods or melt processing methods, and fluoropolymer containing resins applied by liquid methods which comprises applying said coating to the surface of an object comprising the first composition aspect of the invention.
Special mention is made of this process aspect of the invention where the coating is: (a) a resin comprising substantially polyamide 11 or polyamide 12, that is applied by powder coating methods, or (b) a resin comprising substantially any polyamide polymer that is applied by melt processing methods, or (c) a resin comprising substantially poly(vinylidene fluoride) that is applied by liquid methods.
The invention provides in a second composition aspect, a coated object produced by the second process aspect of the invention.